アルカリ土類四水素化物における水素分子の化学的予圧縮効果
Using high-pressure diamond anvil cell experiments combined with Raman spectroscopy, X-ray diffraction, and density functional theory calculations, alkaline-earth tetrahydrides (Ca, Sr, Ba) were synthesized and characterized. These compounds contain both atomic and quasi-molecular hydrogen. The intramolecular H-H stretching frequency decreases progressively from Ca to Sr to Ba under compression, indicating that larger host cations produce longer H-H bonds. Electron localization function analysis reveals two contributing factors: charge transfer from the metal to the H2 units and steric effects imposed by the metal host lattice. The effect is most pronounced in BaH4, where at 50 GPa the H-H bond length approaches values otherwise observed in pure hydrogen only above 275 GPa, demonstrating effective chemical precompression of the molecular hydrogen units.
Charge transfer from the alkaline-earth metal to quasi-molecular H2 units, combined with steric effects of the host lattice, elongates the H-H bond, effectively replicating high-pressure bond lengths at substantially lower applied pressures.
The delivery route is not clearly identifiable from this paper. For hydrogen intake, inhalation is the most efficient route; inhalation, however, carries explosion risk (empirical LFL of 10%; high-concentration devices are not recommended).
See also:
https://h2-papers.org/en/papers/36053162